Bioreactors used in the biological, microbiological and medical field, for example for the perfusion of cultures of animal or human cells or for the creation of bioartificial organs, where the expression “bioartificial organ” is used to designate extracorporeal devices capable of supporting or temporarily compensating for insufficient functions of organs of a human being, have long been known.
Bioreactors used to create bioartificial organs can host cultures of animal or human cells capable of reproducing the specific functions of the organ to be supported.
Merely by way of example, bioreactors are used to create bioartificial livers, which are extracorporeal devices substantially constituted by a filtration unit, which separates the fluid to be processed, plasma or ultrafiltrate, from the corpuscular components of blood drawn from a patient; by a bioreactor, which contains a culture of metabolically active hepatocytes and is crossed by the fluid to be processed; and by a unit for recombining the processed fluid in output from the bioreactor with the corpuscular components of the blood, which is then reinjected into the patient.
The bioreactor must allow contact between the fluid to be processed and the hepatocytes, so that an exchange suitable to rebalance the concentration of the components of the fluid and of the gases dissolved therein occurs, and so that at the same time the passage of hepatocytes or of fragments thereof in said fluid is prevented, in order to avoid patient immunization phenomena.
The first bioreactors used specifically for bioartificial livers were built by using dialysis machines as their model and by using the basic principles of dialysis processes.
There has been a transition from the early flat-membrane bioreactors to the more recent bioreactors with bundles of hollow capillary fibers, on the outside or inside of which the cell cultures are accommodated.
The use of hollow capillary fibers has allowed to improve diffusion and exchange processes between the fluid to be processed and the cell cultures and to provide the oxygen input required for the metabolism of these cultures.
However, these known bioreactors have had some drawbacks, including the fact that the exchange between the cell culture that they host and the fluid to be processed that passes through them occurs unevenly, inconstantly and partially on the useful exchange surface, with a consequent limited utilization of their actual exchange capacity and a reduction of their efficiency.
This is due both to the low pressure at which it is necessary to introduce the fluid to be processed, in order to avoid subjecting the cells of the culture to stresses that would compromise their vitality, and to the shape and configuration of the supporting structure of the cell cultures, which cause a concentration of the exchange at the region where the fluid enters the bioreactor instead of distributing it over the entire useful surface.
Another drawback of known bioreactors is that the useful volume for the cell culture is greatly reduced with respect to their total volume, the former being on the order of one third of the latter; this, combined with the need to have a sufficient cell concentration capable of replacing the functions of the organ to be supported, entails an increase in the overall dimensions of bioreactors.
In order to obviate these drawbacks, bioreactors with hollow capillary fibers are known which are essentially constituted by a substantially tubular container which internally accommodates a cell culture and support structure and is provided, at one end, with a port for the inflow of the fluid to be processed, which is arranged upstream of the structure, and at the opposite end with a port for the outflow of the processed fluid, which is arranged downstream of the structure.
Upstream of the support and culture structure there is a first chamber for collecting the fluid to be processed, which is connected to the outside of the container by means of the inflow port; downstream of the support and culture structure there is a second chamber for collecting the processed fluid, which is connected to the outside of the container by means of the outflow port.
The support and culture structure is constituted by a multilayer panel, which is wound in a spiral around a coupling stem that is substantially coaxial to the container, is internally hollow and has a blind end and another open end that is connected to the outside of said container.
The panel has an edge that is rigidly coupled, by interlocking and/or gluing, to a longitudinal slit formed in the stem, and the opposite edge that is in contact with the inside wall of the container; the opposite ends of the spiral are embedded in a respective containment ring.
The panel is constituted by at least six superimposed flat layers: a first layer, constituted by an order of capillary hollow fibers for the outflow of the processed fluid, which are parallel to the axis of the container and are bent in a U-shape so that their free ends lead into the second collection chamber; a second layer, which is constituted by a permeable and filtering cell support medium; a third layer, which is constituted by a lattice for distribution of the cells to be seeded; a fourth layer, which is identical to the second layer; a fifth layer, which is constituted by an order of capillary hollow fibers for the inflow of the fluid to be processed, which are parallel to the axis of the container and are bent in a U-shape in the opposite direction with respect to the fibers of the first layer, so that their free ends lead into the first collection chamber; and finally, a sixth layer, which is constituted by an impermeable sheet that separates the capillary fibers of the first and fifth layer when the panel is wound in a spiral.
The cells to be seeded in the culture and support structure are inoculated, through the open end of the stem, into the cavity of said stem; the inoculated cells diffuse throughout the structure through the edge of the panel that is fixed to the stem.
Once seeding of the cells has ended, the bioreactor can be used as a bioartificial organ: the fluid to be processed is introduced through the inflow port into the first collection chamber and from there penetrates into the inflow fibers; after saturating them, it passes through their walls, and by following a substantially radial flow it reaches the layer that supports the cells with which the exchange of solutes occurs.
The fluid thus processed, again following a flow that is substantially radial with respect to the axis of the container, reaches the outflow fibers, and penetrates inside them through their walls in order to flow out into the second collection chamber and be evacuated through the outflow port.
These last known bioreactors, while having allowed to overcome the drawbacks noted earlier by allowing to provide a uniform exchange over the entire useful surface and to better utilize the available volume, nonetheless have drawbacks, including the fact that they have a very complex structure, require long, laborious and accurate assembly operations, and require the use of various kinds of material, with a consequent increase in production costs and times.
It is noted, for example, that precise operations for interlocking and bonding the edge of the panel to the central stem with adhesive are required.
Moreover, it is noted that the multilayer panel has a very complex configuration, which requires the superimposition of a plurality of different layers, including an impermeable one that is suitable to separate the hollow inflow fibers from the outflow fibers, so as to avoid any mixing of the fluid to be processed and the already-processed fluid.